One odd thing that sets League of Legends apart from Dota 2 and Heroes of the Storm is the fact that the other games have "characters" who aren't actually a single character. Rather, they're a cluster of individual units controlled RTS-style. A Riot designer now says we shouldn't expect anything like that for League.
The distinction between controlling a single character and multiple units simultaneously might sound like a small one, but I assure you it's not. The weird genius of MOBAs that made League and Dota 2 so successful is the way they have wedded action RPG-style gameplay with an RTS template -- sort of like fusing Diablo and StarCraft into one game. The "two for one" champions in Dota and Heroes are definitely the exception to the games' design trends rather than the rule.
HOTS, for instance, has The Lost Vikings. These are three separate fighters, each with their own health bar and unique traits:
You can send the three vikings in totally different directions across the map -- using them to fill empty lanes, soak up experience from all three lanes at once, or have one of them scout a location independently of the others. These are all very hard things to manage in a MOBA -- again, these games might look likes RTS games, but they're really nothing like them in practice. It's much easier to stick with a single character. The trade-off is having three bodies in a fight instead of one is a powerful asset in its own right. And they can be a lot of fun to play is, particularly if you're the type of person who excels at RTS-style micromanagement of a bunch of different moving parts. Dota 2 has even more characters like this. The Lone Druid, for instance, has a pet bear with his own inventory and set of abilities.
So if these sorts characters work in two of the biggest games in the genre, why wouldn't they work for League?
Daniel Klein, a champion designer at League of Legends developer Riot Games, broached the subject recently on his ask.fm page. He was responding to someone asking if League could have a "2 in 1 champion" similar to Heroes of the Storm's Viking trio. Klein responded maaaaaaaybe, but probably not. Why? Because the idea of selecting multiple controllable units goes against the design principles the game runs on (emphasis added):
Do you think league has a possibility to have a 2 in 1 champion? like the Vikings on Heroes of the Storm Short answer is it's unlikely. Long answer! When we made League, we looked at the obvious inspiration, Dota, and made some baseline changes to the game that Dota, being a War3 mod, couldn't make. One of them is the "stickiness" of self selection. In League, you cannot "unselect" yourself as a unit, and this has a lot of positive implications, but it also means that RTS-like controls are out of scope. This is the most intuitive control scheme for multiple units. So if we wanted to make a champ that was two independently controllable units, we would need to do a LOT of work on the UI / input side. Additionally, many skills learned on this champion would not be transferrable to other champions and no other champions would prepare you for this dual champion. And finally, because brain cycles are a finite resource, there is only so much complexity we could put into the champion's actual kit -- most of its complexity budget would be eaten up already by the mere fact that you're controlling two independent units. TL;DR: I don't think this kind of champion would be a good fit for League, but as always I could be wrong!
Klein makes a lot of good points here -- the sheer complexity of the fact that The Lost Vikings are three separate people means they have almost no special abilities. At the same time, the whole micromanagement side of a game like Dota 2 is part of its core challenge -- and thus part of what makes it fun for all the people who play it. That HOTS could emulate this while still making a character like The Lost Vikings relatively simple when compared to similar units in Dota 2 (like Meepo) is strong evidence that League of Legends could also shave off extraneous material to make any two-for-one champ fit into the game better.
Regardless, I have to respect the fact that Klein is taking a firm game designer-y stance here, rather than just seeing what Riot's competitors are doing and trying to emulate it.